During the telecon today we looked at
http://www.w3.org/2005/rules/wiki/RDF_Combination_Constant_Equivalence_2
and it seems that while that example is supported by the SWC, SWC isn't
saying quite the right thing, here. It says plain literals without
language tags map to xs:string constants, but I think it would be better
to map to rdf:PlainLiteral constants. The difference is actually
invisible to any entailment test (I think? maybe it depends on the
entailment regime?), so in a sense RIF doesn't care, but for interchange
purposes is does matter. In particular, SPARQL, when not doing
entailment, will notice the difference.
Do you remember why it's xs:string now?
This isn't a huge problem, but if there's no compelling reason not to
change it, I think it's more correct to map to rdf:PlainLiterals.
-- Sandro